I don't think that Payless is the best contact for this; I would suggest the shoe designers. I think that this is a great letter, however, and I like that it's concise.
If your daughter's pediatrician would be willing to write prescriptions for her shoes, your insurance probably wouldn't cover them BUT they'd be a medical tax writeoff at the end of the year.
Sounds like your kid's got a mommy who cares. Awesome.